…There has been an observation since the time of the ancients regarding virtue formation (or, habits-of-character formation), namely that we practice what we want to become. It’s like learning a sport, actually, and the same principle applies to all kinds of things in life. When we first try to learn a new skill, it feels stilted. But sure enough, with enough practice, we get good at a particular thing, such that it becomes automatic, even without trying.
And here’s the really cool thing about it, actually: you will find that actions can influence emotions. It’s been shown that people who practice being happy, courteous, loving, etc., will actually start to feel these things simply by virtue of going through the motions. So not only does the skill become developed through repetitive activity, but your emotions will likely also feel happier as a result, and smiling becomes even more natural. It’s a vicious cycle of goodness.